Method for making a passivating coating based on one or more silicon compounds on a ceramic matrix composite reinforced with carbon fibres and ceramic matrix composite reinforced with carbon fibres with such coating

Method for making a silicon compound-based passivating coating on a ceramic matrix composite reinforced with carbon fibres, said method comprising the following steps:

• a) providing a piece to be coated comprising a ceramic matrix composite reinforced with carbon fibres, wherein the ceramic matrix composite reinforced with carbon fibres of the piece to be coated further comprises free silicon and free carbon;
• b) placing said piece to be coated in a closed chamber of an oven;
• c) placing in said closed chamber a predefined load of solid silicon avoiding direct contact between the solid silicon and said piece to be coated;
• d) heating said oven, maintaining inside said chamber predefined medium vacuum conditions, with partial pressure from 5 mbar to 300 mbar, or low vacuum conditions, with partial pressure up to 0.1 mbar, so as to generate from said solid silicon load vapours of silicon inside said closed chamber, which react with one or more substances present on the surface of said piece leading to formation of a surface coating comprising composites of said one or more substances with the solid silicon, wherein said heating is conducted in the presence of a partial nitrogen and/or inert gas pressure, to prevent pressures lower than vapour tension of the free silicon being reached inside said closed chamber and causing vaporization or sublimation of any of the free silicon contained in said piece, and to reduce wettability of the free silicon with respect to the free carbon and thereby limit leakage of any free silicon present inside said piece before formation of said passivating coating;
• e) choosing the partial pressure of the vacuum, temperature inside said closed chamber and exposure times of said piece to the vapours of silicon so as to obtain a predefined thickness of the surface coating on said piece;
• and
• f) cooling said piece once said predefined thickness of the passivating coating has been reached.